The present invention pertains to the diagnostic imaging and radiation-to-electrical signal conversion arts. It finds particular application in conjunction with a two-dimensional detector for computerized tomographic scanners and will be described with particular attention thereto. It is to be appreciated, however, that the invention will also find application in conjunction with conventional x-ray diagnostic systems, fluoroscopic x-ray systems, and other radiation detection systems for medical and non-medical examinations.
A third generation CT scanner includes an x-ray tube which projects a fan-shaped beam of radiation across an examination region. An array of x-ray detectors is disposed across the examination region from the x-ray tube to receive radiation which has passed through the subject. The x-ray source and detectors rotate concurrently around the examination region to collect x-ray attenuation data along a multiplicity of paths.
The x-ray detectors have included scintillation materials which convert received x-rays into light. The scintillation crystals are optically coupled to photomultiplier tubes, photodiodes, or CCD arrays. In single slice scanners, the x-ray beam was collimated into a thin fan beam and the detector included a linear array of detector elements. For faster data acquisition, detectors using two-dimensional arrays have also been utilized. A variety of scintillators have been utilized. Common scintillators include doped cesium iodide (CsI(Tl)), cadmium tungstate (CdWO4), bismuth germanate (Bi4Ge3O2, also known as BGO), and various ceramic scintillators such as Gd2O2S(Pr), (YGd) O (Eu2) or3Gd3Ga5O12(Cr). Cesium iodide scintillators tend to have a relatively long after-glow which interferes with high-speed data collection. Bismuth germanate tends to have a relatively low light output with a less than optimal spectral match to most photodiodes. Cadmium tungstate has a higher output than bismuth germanate, but still higher outputs and better spectral matches to the photodiodes would be advantageous. Ceramic scintillators tend to absorb the emitted fluorescent light so that the optical quantum detection efficiency is low. Thicker layers give disappointingly low light output. Thinner layers do not absorb a very high proportion of the incident x-rays, so that they result in low x-ray quantum detection efficiency and expose the patient to high x-ray dosage.
The present invention contemplates a new and improved x-ray detector and a new and improved diagnostic apparatus and method incorporating an improved radiation detector.
In accordance with one aspect of the present invention, a radiation detector is provided for a medical diagnostic imaging system in which x-rays propagate along a path between a radiation source and the detector. The detector includes a multi-layer scintillator including upper scintillating layers of a relatively longer emission wavelength and permissibly low radiation absorption and lower scintillating layers of high x-ray absorption and permissibly shorter emission wavelength which are substantially transparent to the light emitted by the upper scintillating layers. At least one of the upper scintillating layers is doped zinc selenide. The upper and lower layers are aligned and arranged serially along the radiation path and present substantially equal cross sections. A light sensitive array is optically coupled with a lowest of the lower scintillating layers for viewing the multi-layer scintillator and combining optical outputs of its multiple layers into an analog output signal which adapted to be reconstructed into an image representation.
In accordance with another aspect of the present invention, a radiographic examination system is provided. An x-ray source projects x-rays through an examination region. An x-ray detector is disposed across the examination region from the x-ray source. The x-ray detector includes a doped zinc selenide scintillation layer, an opto-electrical transducer for converting light from the zinc selenide layer into electrical signals, and a light transmissive scintillation layer disposed between the array of opto-electrical elements and the zinc selenide layer.
In accordance with another aspect of the present invention, a radiographic examination system is provided. An x-ray source projects x-rays across an examination region. An x-ray detector is disposed across the x-ray examination region from the x-ray source. The detector includes an array of opto-electrical elements, an array of light transmissive scintillators, and a layer of higher efficiency scintillator material. The array of light transmissive scintillators is disposed on and optically coupled to the array of opto-electrical elements such that each of the opto-electrical elements converts light received from a corresponding transmissive scintillator into an electrical output signal. The layer of higher efficiency scintillator material is optically coupled to the transmissive scintillator array. The higher efficiency scintillator layer is a scintillator material of permissibly limited opacity, higher x-ray conversion efficiency than the transmissive scintillators, and preferably has a better optical match to a peak sensitivity spectrum of the opto-electrical transducers than the transmissive scintillators.
In accordance with another aspect of the present invention, a method of radiographic diagnostic examination is provided. X-rays are propagated through a subject and a first portion of them is converted into first light signals by a zinc selenide scintillator. Concurrently, a second portion of the x-rays which have propagated through the subject and the zinc selenide scintillator are converted into second light signals. The first and second light signals are combined and converted into electrical signals which are reconstructed into an image representation. At least a portion of the image representation is converted into a human-readable display.
One advantage of the present invention resides in its high x-ray conversion efficiency.
Another advantage of the present invention is that it promotes more rapid data acquisition and faster scanning times.
Another advantage of the present invention resides in the improved spectral match between the scintillator and photodiodes.
Still further advantages and benefits of the present invention will become apparent to those of ordinary skill in the art upon reading and understanding the following detailed description of the preferred embodiments.